1. Field of the Invention
The present invention relates to exhaust gas treatment catalysts improved in heat resistance and performance at low temperatures, and also having excellent conversion activity for nitrogen oxides, hydrocarbons, and carbon monoxide.
2. Brief Description of the Prior Art
The conventional exhaust gas treatment catalyst was normally comprising a gamma-alumina support and an active metal supported thereon.
In the case of the conventionally used gamma-alumina support, a high temperature and/or the presence of water vapor will cause sintering of the compound, reduction of the surface area, and lowered activity. Further, the gamma-alumina support suffers from toxicity of sulfur or phosphorus, the pores are clogged, the surface area is reduced, activity is lowered.
In the case of a conventional catalyst synthesized by a gamma-alumina support and an active metal supported thereon, since the activity is extremely reduced at temperatures lower than 300.degree. C., the catalyst merely operates at the condition in which the exhaust gas is sufficiently warmed.